Production of prestressed concrete

ABSTRACT

The production of prestressed concrete is effected by feeding pretensioned reinforcing wires through a station at which fluent concrete is supplied. The fluent concrete is deposited on and around the reinforcing wires and is conveyed along with the wires to a desired location such as a station at which the prestressed concrete product is cut up into sections of appropriate length. The rate of feeding of the concrete and pretensioned reinforcing wires is such that the concrete is either cured or set before, on reaching or after said location.

United States Patent Crowder 1541 PRODUCTION OF PREsTREssEn- CONCRETE [72] Inventor: David Bickerton Crowder, Barkway,

Hertfordshire, England [73] Assignee': Flowcrete Limited, Derby, England [22] Filed: Sept. 29, 1970 [21] Appl. No.: 76,377

[30] Foreign Application Priority Data Sept. 30, 1969 Great Britain ..47,975/69 52 US. Cl...; ..425/111, 264/228 51 Int. C1. ..B28b 23/04 58 Field of Search ..25/118 T; 264/228; 52/223; 425/111 56] References Cited UNITED STATES PATENTS 2,394,228 2/1946 Barber et a1 ..2s/11s T x 3,055,073 9/1962 Gerwick, Jr ..'.25/118 T X 1451 Sept. 26, 1972 11/1966 Oakden ..25/118 T 3,181,222 5/1965 Palmer ..264/228 X 3,276,092 10/1966 Pankow ..25/1 18 T 3,475,529 10/1969 Lacy ..425/ll1 X 3,647,308 3/1972 Yost ..425/1 1 1 Primary Examiner-Robert L. Spicer, Jr. Attorney-Holman & Stern 57 ABSTRACT The production of prestressed concrete is effected by feeding pretensioned reinforcing wires through a station at which fluent-concrete is supplied. The fluent concrete is deposited on and around the reinforcing wires and is conveyed along with the wires to a desired location such as a station at which the prestressed concrete product is cut up into sections of appropriate length, The rate of feeding of the concrete and pretensioned reinforcing wires is such that the concrete is either cured or set before, on reaching or after said location.

5 Claims, 4 Drawing Figures PATENTED SEP 26 1972 SHEET 3 [1F 3 A Treader;

PRODUCTION OF PRESTRESSED CONCRETE BACKGROUND OF THE INVENTION This invention relates to the production of prestressed concrete.

With present methods of producing prestressed concrete the prestressed reinforcing wires are laid in a mold or on a molding bed and a travelling hopper is progressed thereover depositing concrete onto and around the wires and the concrete remains in the mold or on the molding bed until it is cured or set. This is disadvantageous since the mold or molding bed is not available for further production until curing or setting is completed and clearing of the concrete product from the mold or molding bed is effected, and therefore the rate of production is relatively slow.

It is an object of the present invention to provide a method of and apparatus for producing prestressed concrete at a higher rate than hitherto.

SUMMARY OF THE INVENTION According to the present invention, there is provided a method of producing prestressed concrete comprising the steps of feeding pretensioned reinforcing wires past a supply of fluent concrete, depositing fluent concrete on and around the pretensioned reinforcing wires, and conveying'the concrete product and embedded pretensioned wires to an output location at a rate such that the concrete is cured or set either after reaching or on reached said location or such earlier location as is desired.

Also according to the present invention, there is provided apparatus for producing prestressed concrete comprising a molding conveyor having an output location at or adjacent one end and means for supplying fluent concrete onto the conveyor at or adjacent to the other end, and means for traversing pretensioned reinforcing wires over the conveyor in the direction of movement of the latter, with the conveyor speed being such that the concrete reaches the output location before being hardened or is hardened on reaching the output location or such earlier location as is desired.

The apparatus may comprise two advancing devices interacting with the molding conveyor on the concrete product and prestressing wires to permit continuous production.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic perspective view of apparatus in accordance with the present invention;

FIG. 2 is a fragmentary perspective view of part of the conveyor;

F IG. 3 is a perspective view and two interacting advancing devices; and,

FIG. 4 is a sectional view of a wire stressing jack.

DETAILED DESCRIPTION OF THE INVENTION In a batch producing apparatus there is a molding conveyor which may have sides or which may simply be a flat bed conveyor.

The intermediate part of the conveyor 10 is preferably made by a precast concrete trough 11 (FIG.

2) with two longitudinal upstands 12 across which are precast trough units 13 with the ends and undersides of this part blocked so that the opening into the trough is within the distance between the upstands 12.

The top surface of the units 13 is accurately cast to a flat, true plane, and the top surface fixed to a jig while assembling so that a joint 14 of epoxy or polyester resin between the units and upstands takes up inaccuracies. A conveyor belt 15 rests on the top surface of the trough units 13 which are made of porous concrete on the contact face, or are perforated with holes 16.

The trough units 13 are secured in position by bolts 17 and the joint between adjacent trough units 13 is sealed with a rubber strip.

Water can be pumped at a sufficient rate by any convenient means into space 18' between the upstands 12 and flows up through the units 13 and through the holes 16 lifting the belt 15 off the surface of the units 13 creating a continuous film of water on which the belt rides. The surplus water flows out at the sides of the belt, and the V slots formed by the sloping sides of the units 13. This water then returns to, for example, the

pump via troughs 19 formed in the construction.

If it is desired to heat a concrete product 20 to produce accelerated hardening of the concrete, the water used to lift the conveyor belt 15 is heated to the temperature necessary to achieve this end.

The trough 11 is covered with insulation 21 on the sides and base, and has a removable insulating top cover 22 to reduce heat losses.

The trough 11 is suspended from cross bars 23 at about 15 foot centers which are supported on struts 24 each with a screwed rod 25 on top engaging with a nut 26 on either side of the cross bar 23 to enable the trough 11 to be levelled, and to correct any subsequent subsidence.

The struts 24 are preferably made out of R.S.J. section in which the flanges are cut away locally at 27 to provide hinge points to allow for expansion and contraction of the trough 11.

The trough 11 is set to a fall from the casting end of the conveyor which is greater than the coefficient of friction of the conveyor belt 15 on the water bearing to ensure that the belt is held back by a drive drum 28. This is to ensure that increasing stretch in the belt, due to loading takes place as the belt leaves the drive drum before concrete is cast onto the belt.

The trough 11 also acts as a strut to take the loads of the conveyor belt tension and the tension in the stressing wires or stands, hence doing away with the large end anchorages that would otherwise be needed.

The advantages of this conveyor construction are ease of lining up the conveyor to the accuracy required. There is no tendency for the conveyor belt to deflect sideways due to the idler rollers being at a slight angle on plan to the direction of belt travel. There are no the speed at which the apparatus can deliver molded concrete.

When the molded concrete 20 reaches the output end of the conveyor 10, the conveyor is stopped until the concrete 20 has reached the desired strength for stress transfer of prestressing wires 31 to the concrete.

At the input end of the conveyor there is provided a number of supply reels 32 of reinforcing wire 31.

Each reinforcing wire 31 passes from its reel 32 through a movable crosshead 33 initially located in front of andadjacent to the casting unit 29, on top of the conveyor 10, and is anchored .by temporary grips 34 to the crosshead 33. Each of the reinforcing wires 31 then pass down the outside edges of the conveyor and around a pulley 35 or the like at the output end of the conveyor 10, back along the underside of the conveyor, during which they are offset by guides 36 towards their desired position in the width of the unit to be produced. The wires are returned around a driven drum 37 at the input end of. the conveyor 10 and the ends of the wires are then anchored to the crosshead 33 as indicated at 38. The pulleys 35 or the like at the output end of the conveyor are then moved outwards by means of hydraulic jacks 39 or the like, to put the desired initial tension into the closed loop produced by anchoring the wires 31 to the crosshead 33.

The drum 37 at the input end of the conveyor is driven in synchronism with the molding conveyor drive drum 28 to feed the prestressing 'wires at the same linear speed as the conveyor 10.

This can be effected either by a positive drive of correct ratio or by means of a torque limiting drive which is set to just overcome the frictional resistance of the system, and movement of the wires or strands 31 is governed by temporarily fixing the crosshead 33 to the conveyor belt 15.

There may be one or more drums 37 at the conveyor input end when it is desired to place wires or strands 31 at different levels in the concrete product being cast.

In use, the reinforcing wires 31 are threaded in the apparatus as described and the jacks 39 actuated to apply the required stress to the wires. Fluent concrete is then deposited and formed into the desired shape on the molding conveyor 10 in a regulated manner, with the conveyor 10 and drum 37 being driven so that the product 20 being cast with its reinforcing wires 31 is advanced from the input to the output end of the conveyor carrying the crosshead 33 with the conveyor 10.

the wires out sideways from the slots in the crosshead and is replaced at the starting position where the wires 31 are again anchored to it by the temporary grips 34. The cycle is repeated with the hardened concrete product previously cast being removed intact or cut to lengths desired by means of a moving saw which travels with the concrete while cutting, and returns to the starting position on completion of the out ready for the next cut to be made.

The number of wires can be varied as desired between batches by only anchoring those wires required to the crosshead.

In a continuously producing machine, which is substantially as described with reference to FIGS. 1 and 2, i

there is again a molding conveyor, a drum at the input end of the conveyor driven in synchronism with the conveyor and reels of reinforcing wires at the input end of the conveyor. In this instance, however, (see FIGS. 3 and 4) the machine is provided with two longitudinally spaced advancing devices 40 and 40A each having a jack or like clamp 41 for gripping the concrete product and wire-stressing jacks 42 and 42A each with a clamping head or collet 43.

The path of each reinforcing wire 31 is from its reel, along the length of the conveyor through the open clamping heads of the corresponding stressing jacks of i the two advancing devices around an idler pulley at the output end of the conveyor around the driven drum into the length of concrete product being cast.

The two advancing devices 40 and 40A reciprocate longitudinally of the conveyor over fixed paths. 7

Each advancing device 40, 40A is hydraulically operated and is connected to a hydraulic jack 43, 43A. The advancing devices 40, 40A operate in the following manner.

When the crosshead 33 and the concrete 20 reach the output end of the conveyor 10, the process is stopped until the concrete has reached the desired strength for stress transfer.

When the prestressed concrete product on the conveyor is wholly set or cured, the jacks 39 are released allowing the hardened concrete to hold the stress in the wires 31 thus prestressing the concrete product 20. The crosshead 33 is removed from the wires 31 by sliding The advancing device 40 operates a switch 44 which causes oil to be released from the jack 43A and oil to be pumped into a port 45A of the advancing device 40A forcing the plate jack 41 to grip the product 20. On the required pressure being reached, oil is pumped into a port 46 of jacks 42A causing collets 43 to grip the wire or strand 31 and to tension the wire to the required tension. This is controlled by regulating oil pressure in the jack 42A. When the preset pressure is reached in the jacks 42A oil is released from .the clamp 41 of the advancing device 40 and oil is pumped into the port 47 of the jacks 42 causing collets 43 to be released from the wires. On preset pressure being reached at the port 47 which will ensure release of the collets 43, oil is pumped into the jack 43 to return the advancing device 40 to its starting position. Meanwhile the advancing device 43A travels forward with the product 20 until it trips switch 44A when the above sequence changes over to advancing device 40.

The advancing devices are carried along by the movement of the product 20 towards the outgoing end of the conveyor.

The switches 44 and 44A are part of a hydraulic control circuit of conventional design.

The functioning of the jacks 42, 42A is as follows:

Oil enters the port 46 of each jack, drives a piston assembly 48 forward, and a spring 49 pushes the split collet 43 into the cone in a piston rod 50 gripping the prestressing wire or strand 31 and loading the prestressing wire to the required tension.

On oil entering port 47, the piston 48 retracts until the collets 43 hit the inner part of cylinder assembly thus pushing the collets out of the cone, releasing the grip on the prestressing wire or strand 31 and allowing the advancing device to be moved back to its starting positlon.

These advancing devices operate switches of a control system which sequentially operates the various jacks and the means for reciprocating the advancing devices as described.

In use, the initial production to fill the conveyor belt with the product is carried out as for batch production. When the concrete has sufficiently hardened, the initial stress in the wires is released by the hydraulic jacks or other device acting on the pulleys at the output end of the conveyor and the crosshead removed. The hardened concrete product and reinforcing wires are then threaded through the two advancing devices, the product and reinforcing wires being gripped by the jacks of the first advancing device and the wires stressed. The line is then started and the first device moves along its path towards the output end of the conveyor, while the second device (i.e. that nearer the output end of the conveyor) moves along its path towards the input end of the conveyor. When the two devices are adjacent, the first device trips a switch causing the jacks of the second device to grip the hardened product and stress the wires while the jacks of the first device are released. The two devices then move away from one another, the second device advancing the hardened concrete product. When the devices reach the opposed and remote ends of their paths, the second device trips a switch causing the jacks of thefirst device to grip the product and stress the wires while the jacks of the second device are released.

The devices then approach each other with the first device advancing the hardened concrete product.

Thus, the devices serve to advance the concrete product in turn towards the output end of the conveyor and allow fresh wire into the system under tension.

When the concrete product has passed through the advancing devices it can be sawn to length by means of a moving saw.

By the methods described the forces due to prestressing the wires are balanced and the only driving force to move both the conveyor and the wires is that required to overcome friction.

Prestressing strand may be used in place of prestressing wire.

What is claimed is:' V

1. Apparatus for producing prestressed concrete comprising a molding conveyor, means in the conveyor for providing a fluid film for supporting the concrete product, an output location at or adjacent one end of said conveyor, means for supplying fluent concrete onto the conveyor at or. adjacent to the other end of said conveyor, and means for traversing pretensioned reinforcing wires over the conveyor in the direction of movement of the latter.

2. The apparatus as claimed in claim 1, including means for supplying reinforcing wires, wire moving means securable to the conveyor, and means for looping the wires from the supply means along the conveyor around a tensioning means and back along the conveyor for securement to the wire moving means which move the wires with the concrete product being cast.

3. The apparatus as claimed in claim 2, comprising at least two concrete product advancing means including means for clamping the concrete product and means for tensioning the wires, the arrangement being such that while one advancing means is progressing and tensioning the wires, the other advancing means is taking up a starting position for product progression and wire tensioning, each advancing means including a hydraulically operable product clamp, and hydraulically operable wire tensioning jacks and a hydraulic jack for selectively moving each product advancing means in a direction opposite to that in which the concrete product is moved.

4. Apparatus for producing prestressed concrete products comprising a molding conveyor, an output location at or adjacentone end of said conveyor, means for supplying fluent concrete onto the conveyor at or adjacent to the other end of the conveyor, means for supplying reinforcing wires to the conveyor, wire moving means secured to the conveyor, and means for looping the wires from the supply means along the conveyor around a tensioning means and back along the conveyor for securement to the wire moving means which move the wires with the product being cast in the direction of movement of the conveyor.

5. Apparatus for producing prestressed concrete products comprising a molding conveyor, means for supplying fluent concrete onto the conveyor adjacent one end, means for moving the concrete product being cast along the conveyor away from the fluent concrete supplying means, means adjacent the casting end of the conveyor for supplying reinforcing wires for the concrete product being cast, means adjacent the other end of the conveyor around which the wires can be looped, means for moving the looping means to apply a tensioning force to the reinforcing wires, rotatable means adjacent the casting end of the conveyor and between said end and the reinforcing wire supplying means and around which the reinforcing wires returned from the looping means are once again looped before being passed through the fluent concrete on the conveyor and secured to the concrete product moving means thus to move the concrete product and reinforcing wires simultaneously along the conveyor. 

1. Apparatus for producing prestressed concrete comprising a molding conveyor, means in the conveyor for providing a fluid film for supporting the concrete product, an output location at or adjacent one end of said conveyor, means for supplying fluent concrete onto the conveyor at or adjacent to the other end of said conveyor, and means for traversing pretensioned reinforcing wires over the conveyor in the direction of movement of the latter.
 2. The apparatus as claimed in claim 1, including means for supplying reinforcing wires, wire moving means securable to the conveyor, and means for looping the wires from the supply means along the conveyor around a tensioning means and back along the conveyor for securement to the wire moving means which move the wires with the concrete product being cast.
 3. The apparatus as claimed in claim 2, comprising at least two concrete product advancing means including means for clamping the concrete product and means for tensioning the wires, the arrangement being such that while one advancing means is progressing and tensioning the wires, the other advancing means is taking up a starting position for product progression and wire tensioning, each advancing means including a hydraulically operable product clamp, and hydraulically operable wire tensioning jacks and a hydraulic jack for selectively moving each product advancing means in a direction opposite to that in which the concrete product is moved.
 4. Apparatus for producing prestressed concrete products comprising a molding conveyor, an output location at or adjacent one end of said conveyor, means for supplying fluent concrete onto the conveyor at or adjacent to the other end of the conveyor, means for supplying reinforcing wires to the conveyor, wire moving means secured to the conveyor, and means for looping the wires from the supply means along the conveyor around a tensioning means and back along the conveyor for securement to the wire moving means which move the wires with the product being cast in the direction of movement of the conveyor.
 5. Apparatus for producing prestressed concrete products comprising a molding conveyor, means for supplying fluent concrete onto the conveyor adjacent one end, means for moving the concrete product being cast along the conveyor away from the fluent concrete supplying means, means adjacent the casting end of the conveyor for supplying reinforcing wires for the concrete product being cast, means adjacent the other end of the conveyor around which the wires can be looped, means for moving the looping means to apply a tensioning force to the reinforcing wires, rotatable means adjacent the casting end of the conveyor and between said end and the reinforcing wire supplying means and around which the reinforcing wires returned from the looping means are once again looped before being passed through the fluent concrete on the conveyor and secured to the concrete product moving means thus to move the concrete product and reinforcing wires simultaneously along the conveyor. 